A body fat measurement device of a type which performs measurement by wrapping a belt around the abdomen of a subject has high measurement accuracy compared to a body fat measurement device of a built-in type, in weighing scales, or the like, and is used in periodic examinations, and the like. A visceral fat measurement device which uses this measurement method, namely, an abdominal impedance method, has been proposed before by the present applicants in Patent Document 1.
In the abdominal impedance method described in Patent Document 1, a pair of current application electrodes are placed on the front and back of the subject, more specifically, on the center of the subject's abdomen (navel) and the center of the subject's back (spine), and a current is passed in the front/rear direction through the subject's abdomen. Furthermore, a pair of voltage measurement electrodes are placed on the subject at staggered positions in the front and back of the body (the sides of the subject), and the abdominal impedance is calculated from the voltage between the voltage measurement electrodes when a uniform current is passed from the current application electrodes. An amount of visceral fat is measured from this abdominal impedance.
Moreover, in the abdominal impedance method described in Patent Document 1, the subcutaneous fat thickness is measured separately, and the amount of visceral fat is corrected by this measured subcutaneous fat thickness. By this means, the effects due to difference in the subcutaneous fat thickness are eliminated and the measurement accuracy of the amount of visceral fat is improved. In Patent Document 1, desirably, an optical sensor is used as subcutaneous fat thickness measurement means.
In this way, a sensor, or the like, for measuring parameters other than the abdominal impedance such as the subcutaneous fat thickness, are attached to the subject's body, apart from the current application electrodes and the voltage measurement electrodes. Signal wires are extracted from the electrodes and the sensor and are connected to a measurement device. A current is supplied to the current application electrodes by the measurement device, and the amount of visceral fat is measured from the voltages detected by the voltage measurement electrodes and the sensor, and the subcutaneous fat thickness.
In this way, if a sensor for measuring parameters other than the abdominal impedance is attached to a subject's body, apart from current application electrodes and voltage measurement electrodes which are used in order to measure abdominal impedance, then it is necessary to connect a large number of signal wires between the subject and the measurement device, and therefore the arrangement of the signal wiring becomes complicated, usability becomes worse, and the cost of the signal cables increases.
Therefore, from the viewpoint of usability and cost, it is desirable to connect the electrodes and sensor with the measurement device by using a multi-core cable in which a plurality of core wires are bunched together inside a single insulating coating. More specifically, it is desirable to form the core wires for the current application electrodes and the voltage measurement electrodes, and the core wire for the another measurement means, in an integrated fashion inside the same insulating coating.
In a body fat measurement device of a type which is built into weighing scales, for example, the impedance is measured, for example, between the legs of a subject standing on the scales, or between electrodes gripped by the subject's hands or in contact with the user's feet. Therefore, the impedance measurement path becomes long, as a result of which the measurement impedance becomes several hundred Ω, for example.
On the other hand, in a device which measures the amount of body fat from the abdominal impedance, the impedance is measured across a short distance between the subject's sides, and is one several hundredth of the impedance in a measurement device built into a weighing scales, while the measurement voltage is only several mV.
Therefore, if a multi-core cable is used and the core wires for the current application electrodes and the voltage measurement electrodes, and a core wire for another measurement means are bunched inside a single insulating coating, then the wire-to-wire capacitance and unwanted radiation from the core wire for the other measurement means has a great effect on the weak measurement voltage. Consequently, the accuracy of the voltage measurement declines and there is a risk that the measurement accuracy of the abdominal impedance will decline.
Patent Document 1: Japanese Patent Application Publication No. 2007-151619